Posted by: Scott McCullough | August 30, 2011

Foundation Formwork

Hurricane Irene was a dud in New Hampshire.  Or at least in central New Hampshire.  If nobody told me  there was a tropical storm on the way, I would have thought that it was just a heavy rainstorm.  We had gone ahead and installed the portion of the perimeter drain that runs out to daylight on Saturday morning.  Which turned out to be a good idea with all of the rain we had.  Our excavator dug a small trench during the storm Sunday morning to help the water to run out and down from the south side of the house.  No trees were blown down on the property, which wasn’t surprising with the small amount of wind we had.  But, we don’t regret waiting until yesterday to have the foundation formwork go up.  For all we knew anything could have happened, and turned this first phase of our project into a nightmare.

Monday morning Jess’s Dad and I delivered the Thermomass rigid insulation panels to the site that we had stored in a barn over the weekend.  Within a few hours Sonny and his crew had made some progress on erecting the formwork and insulation.

This foundation includes a layer of rigid insulation poured into the middle of the concrete formwork.  Thermomass is the company that has created a fiber cement standoff product that is inserted into the panels which keeps the rigid in the middle of the forms.  The widths of the rigid panels coincides with the widths of the concrete forms, each 2 foot panel has 2 rows of fiber cement standoffs.  One task that seems to be taking some time is physically inserting the standoffs into the plastic grommets that come set into the panels.  This has to be done on-site, if it were done beforehand then transporting the panels would be very difficult.  Sonny mentioned that the other pain is figuring for and cutting down the widths of the panels to accommodate for the dimensions of the foundation walls.  Reason being that each panel should still have 2 rows of standoffs, even when cut down.  If not, then the panel has to be taped on all 4 sides to the adjacent panel.

This system ends up needing more reinforcing bar than most foundations because of there being 2 layers of 4″ concrete, most of which is concentrated on the inside layer, including the footing dowels.  And as it turns out we will need a pump truck.  If the walls were 8″ or 10″ thick the foundation crew could pull the concrete around the foundation while is was being poured.  But these narrow wythes of concrete and all its’ rebar do not allow for pulling of the mix around the foundation.  A pump truck and its’ tall boom can easily reach all of the walls.  The wythes also require that the pour is a wetter self consolidating concrete, with about an 8 slump (http://en.wikipedia.org/wiki/Concrete_slump_test#United_States).

By the end of the day they had almost all of the panels erected.  The pump truck is scheduled for 1:00 tomorrow, so they’ll have plenty of time to install the remaining panels tomorrow morning.

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Responses

  1. Thank you for posting these pictures Scott. I can show these to my dad who was curious about the standoffs…


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